Reagents : 



The same as those listed under 

 Total Only. 



Nitrate-Nitrite 



We used the method of Zwicker and 

 Robinson (1944) as modified by Marvin (1955 

 b) for the determination of nitrate-nitrite. 



The steps that were involved in the 

 determination are as follows: 



1. Remove frozen samples from cold 

 storage and thaw by placing in front of an 

 electric fsin. Thaw 24 samples at a time. 



2. While samples are thawing, set up 

 the required number of 10-railliliter pyrex 

 test tubes to take care of duplicate analy- 

 ses from each vial. CleEun the cap-glass 

 junction of each sample bottle before open- 

 ing. 



3. If the range of nitrate cQjticentra- 

 tion is unknown, proceed as follows— : 



least 15 mixing tubes in rotation, 

 allowing each one to drain after use. 



e. Store samples in darkness for 

 3 to 5 hours, then check color density 

 with a Fisher a. c. electrophotometer 

 equipped 3-milliliter micro cells and 

 a 525 B filter. 



f. Check the results against 

 standard samples run with the unknown 

 samples. 



Strychnidine reagent: 



Dissolve 0.3 millimole of strych- 

 nidine in a liter of 36N Du Pont c. p. 



V°4- 



Nitrite 



For the determination of nitrite in 

 sea water, we used the method of Robinson 

 and Thompson (1948b). 



Steps involved in the determination 



a. With a 1-milliliter pipette, 

 transfer 1 ml. of sample into its 

 designated test tube. 



b. With a 2-milliliter automatic 

 pipette, add 2 ml. of distilled water 

 to each of the 10-milliliter tubes. 



c. Using a 5-milliliter pipette, 

 add 3 ml. of strychnidine reagent to 

 each tube. To prevent boiling during 

 this addition, tilt the tube about 45° 

 and allow the reagent to run down the 

 inside so that it forms a layer under 

 the water sample. Perform this step 

 carefully to avoid unnecessary mixing 

 of reagent and sample. 



d. With another 10-milliliter 

 pyrex tube, mix by gently pouring the 

 contents of each tube into the mixing 

 tube and back again only once. Use 



2/ If samples are known to be low in ni- 

 trate concentration (below 8 pg at /l), 

 proceed as in item No. 3, but omit step 

 "a" and add 3 ml. of sajnple in step "b" 

 rather than 2 ml. of distilled water. 



1. Remove frozen samples from cold 

 storage and thaw by placing in front of an 

 electric fan. Thaw 24 samples at a time. 



2. While samples are thawing, set up 

 the number of 60-railliliter Erlenmeyer 

 flasks required to make duplicate analyses 

 of each sample. 



3. When samples have thawed to room 

 temperature, clean the cap-glass junction 

 with a jet of distilled water and remove 

 the cap. 



4. Add 25 ml. of sample to each flask 

 with a large bore 24-milliliter graduated 

 pipette. 



5. Prepare working reagent by mixing 

 together equal volumes of the alpha-naph- 

 thylamine and sulfanilic acid reagents. 



6. Add 1 ml. of the working reagent 

 to each sample and swirl flask gently after 

 each addition. 



7. After 1/2 hour determine the color 

 density with a Fisher a. c. electrophoto- 

 meter, using a 525 B filter. If the salini- 

 ty of the sample is zero or close to zero, 

 allow 2 to 3 hours for color development. 



